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IIT Jodhpur

Geogrids embedded in fill materials are checked against pullout failure through standard pullout testing methodology. The test determines the pullout interaction coefficient which is critical in fixing the embedment length of geogrids in mechanically stabilized earth walls. This paper proposes prediction of pullout interaction coefficient using data driven machine learning regression algorithms. The study primarily focusses on using extreme gradient boosting (XGBoost) method for prediction. A data set containing 220 test results from the literature has been used for training and testing. Predicted results of XGBoost have been compared with the results of random forest (RF) ensemble learning based algorithm. The predictions of XGBoost model indicates 85% accuracy and that of RF model shows 77% accuracy, indicating significantly superior and robust prediction through XGBoost above RF model. The importance analysis indicates that normal stress is the most significant factor that influences the pullout interaction coefficients. Subsequently pullout tests have been performed on geogrid embedded in four different fill materials at three normal stresses. The proposed XGBoost model gives 90% accuracy in prediction of pullout interaction coefficient compared to laboratory test results. Finally, an open-source graphical user interface based on the XGBoost model has been created for preliminary estimation of the pullout interaction coefficient of geogrid at different test conditions.

Department of Civil & Infrastructure Engineering

World University root node

Geotextiles and Geomembranes

Prediction of pullout interaction coefficient of geogrids by extreme gradient boosting model

Pullout behaviour of geogrids is critical to understand in the design of mechanically stabilized earth walls. The pullout coefficients are determined through laboratory testing on geogrids embedded in structural fill. Random forest (RF) is a data-driven ensemble learning method that uses decision trees for classification and regression tasks. In the present study, the use of random forest regression technique for estimation of pullout coefficient of geogrid embedded in different structural fills and at variable normal stress based on 198 test results has been investigated using five-fold cross-validation. 80 % of the data has been trained on the model algorithm and the accuracy of the model is then tested on 20 % of the remaining dataset. The performance of the model has been checked using statistical indices, namely R2, mean square error, as well as external validation methods. The validity of the model has also been checked against laboratory tests conducted on geogrid embedded in four different fills. The results of the RF model have been compared to results obtained with three other regression models namely, Multivariate Adaptive Regression Splines, Multilayer Perceptron, and Decision Tree Regressor. The results demonstrate superiority of the RF-based regression model in predicting pullout coefficient values of geogrid. © 2021 Thomas Telford Ltd.

Geosynthetics International

Novel Application of Machine Learning for Estimation of Pullout Coefficient of Geogrid

In the recent past, geotechnical applications of CCR is the major focus area in the construction industries. However, the economics of a project and environmental safety are some of the key issues, that still need to be addressed. This research work focusses on the comprehensive assessment of the economic and ecological sustainability of bulk utilization of CCR in geotechnical applications. Physical, mechanical, and physicochemical properties of different types of CCR were determined and compared with locally available natural soil. The results reveal that all CCR samples were non-plastic, exhibited low sensitivity to moisture content, negligible crushing during compaction, and displayed significant shear strength (φ ≥ 30°). All CCR demonstrated an alkaline pH that satisfied the requirements of a fill material. The environmental risk associated with the application of CCR was assessed through leachability tests as per EN 124057–4 (2002). The results revealed that CCR is safe for disposal in inert landfills as per European Council Decision 2003/33/EC guidelines, due to low risk to the environment. The cost estimation suggests that CCR is comparably very economical if available within 5 km of a construction site. The findings of the study clearly revealed that the application of CCR is cost-effective as well as environmentally safe and a sustainable alternative to the natural soil. © 2020 Elsevier Ltd

Journal of Cleaner Production

Comprehensive assessment of cleaner, sustainable and cost-effective use of coal combustion residue (CCR) in geotechnical applications

IIT Delhi

Feasibility of using coal bottom ash, pond ash or fly ash as structural fill material in mechanically stabilized earth walls

IN Patent App. 201,811,027,187

APPARATUS AND METHOD FOR MEASURING PULLOUT RESISTANCE OF A REINFORCING ELEMENT OF REINFORCED SOIL STRUCTURES

Currently, nearly 170 million tonnes of coal ash is generated annually in India from 85 thermal power plants, and because of the limited availability of land, vertical expansions of ash dykes are unavoidable. The present paper compares the variability in engineering behaviour of coal ash from two different thermal power plants (TPP) A and B and highlights the influence of the variability in coarse particle content on design of ash dykes. Using the geotechnical properties of compacted ash as well as hydraulically deposited ash, ash dyke sections have been designed and a series of stability runs are carried out to map the factor of safety at various stages of ash dyke raising. The results indicate that slopes of ash dykes have to be made flatter as bottom ash content decreases in pond ash due to increased utilization or separate storage of bottom ash. © Springer Nature Singapore Pte Ltd 2019.

Geotechnical Characterisation and Geoenvironmental Engineering

Influence of engineering behaviour of coal ash on design of ash dykes

The paper describes the interface behaviour of bottom ash, obtained from two thermal power plants, and geogrid for possible utilization as a reinforced fill material in reinforced soil structures. Pullout tests were conducted on polyester geogrid embedded in compacted bottom ash samples as per ASTM D6706-01. Locally available natural sand was used as a reference material. The pullout resistance offered by geogrid embedded in bottom ash was almost identical to that in sand. In order to study the influence of placement condition of the material on pullout resistance, test were conducted on uncompacted fill materials. Pullout resistance offered by geogrids embedded in uncompacted specimen reduced by 30–60% than that at the compacted condition. © 2019 Elsevier Ltd

Bottom ash as a backfill material in reinforced soil structures

This paper describes a series of pullout tests that were carried out to investigate the role of transverse and longitudinal members (T & L-members) on pullout resistance of a polyester (PET) geogrid. Pullout tests were conducted on four different geogrid configurations with 0, 4, 8 and 16 T-members at three normal stress embedded in bottom ash and fly ash. The pullout resistance increased with increase in number of T-members and normal stress. However, due to different average particle size, the bearing resistance offered by T-members triggers in fly ash earlier than that in bottom ash. Tests were also conducted to study the influence of spacing and number of L-members. It was observed that the zone of influence of individual L-members overlap at close spacing that reduces the pullout load. This study demonstrates that T-members contribute almost 30–60% towards pullout resistance and exhibit higher contribution at larger confinement stress. © 2019 Elsevier Ltd

Measurement

Measurement of role of transverse and longitudinal members on pullout resistance of PET geogrid

Stick-slip behavior was observed while characterizing the shear strength of fly ash collected from a thermal power plant at Delhi, India. Stick-slip oscillations of the shear stress were observed in the shear-deformation curve of fly ash. Pullout tests were carried out on geogrid embedded in compacted dry fly ash to determine the soil-geosynthetic interaction parameters. The pullout test results also exhibited stick-slip oscillations. Subsequently, triaxial tests were conducted to study the influence of strain rate and confining pressure on the stick-slip motion of shear stress. The amplitude of stick-slip oscillations increased with increasing confining pressure whereas decreased with increasing strain rate. In addition to fly ash, the tests were also conducted on a locally available Delhi silt soil to study the influence of particle morphology on stick-slip oscillation of shear stress. These results indicated that due to stick-slip motion, it is not possible to identify a true peak value of shear strength of fly ash. This should be considered while designing a mechanically stabilized earth wall and slope with fly ash as a backfill material. © 2019, © 2019 Taylor & Francis Group, LLC.

Particulate Science and Technology

Stick-slip behavior of dry fly ash

Coal combustion residue (CCR) has gained considerable acceptance in civil engineering applications, mainly in the cement industry and brick manufacturing. However, despite an increasing application of CCR, a large proportion remains unutilized globally. This research focuses on the feasibility of using fly ash, bottom ash, and their mixtures as a filling material in reinforced soil structures (RSS). The physical, mechanical characterization of the materials, along with the pullout resistance behavior of the interface between the CCR and a uniaxial polyester geogrid was studied. The grain size distribution tests showed the presence of 80% silt particles in fly ash and 7% in bottom ash. All the CCR samples were non-plastic in nature, and direct shear test results revealed that well compacted CCR samples offer similar shear strength as that of natural soils used as backfill in RSS. The leachability tests of CCR were carried out as per EN 12457–4 (2002) for the assessment of environmental risk. The results revealed that the leachable toxic contents in CCR remained quite below than the standard prescribed limits defined by the European Council Decision 2003/33/EC. The interaction coefficient values for a bottom ash-geogrid interface, obtained from the pullout test, match well with the results of natural/conventional fill material. The interaction coefficient value for the fly ash-geogrid interface was the lowest amongst the materials tested i. e 0.28 at 80 kPa, which is greater than the value recommended by JTJ015-91. The finding of the study demonstrated the suitability of using CCR as an economical, environmentally safe and sustainable structural fill material behind RSS. © 2019 Elsevier Ltd

Coal Combustion Residue as Structural Fill Material for Reinforced Soil Structures

This paper describes the results of laboratory study on pullout behavior of a polyester geogrid embedded in pond ash. The objective was to assess the feasibility of utilization of ash available in abundant quantity at thermal power plants as a fill material in reinforced soil structures (RSS). The ash does not satisfy the gradation requirements but satisfies the physical and shear strength properties recommended for use in RSS by FHWA and BS:8006. Pullout tests were then carried out as per ASTM D6706 at three normal stresses of 20 kPa, 40 kPa, and 80 kPa. The obtained results were then compared with those of geogrid embedded in reference fill material, Yamuna sand. The study reveals that although pond ash does not satisfy the gradation requirements of a suitable backfill material, the pullout resistance offered by geogrid embedded in pond ash was almost identical to that in sand. © 2019 American Society of Civil Engineers.

Geo-Congress 2019 GSP

Utilization of Pond Ash as Structural Fill Material in Reinforced Soil Structures

In this paper efforts have been made to understand the influence of unit weight of slurry-deposited coal ash on the slope stability of ash dykes raised by upstream method. Using the geotechnical properties of compacted ash as well as slurry-deposited ash, a series of stability analysis have been carried out to identify the critical factor of safety for incrementally raised ash dykes. A 19 m high ash pond in Eastern India had been incrementally raised to its current elevation, by upstream method in four raisings. The ash pond was to be further raised by providing two raisings (5th and 6th) of 3 m each making the ash pond 25 m high. Slope stability analysis of downstream slope of the dykes was carried out for steady state seepage condition using effective stress parameters for the ash as well as foundation soil. For the 5th and 6th raising the critical failure surface was observed to pass predominantly through slurry deposited ash and the foundation soil beneath it. The factor of safety (FOS) was observed to be low on account of the low unit weight as well as the low shear strength of ash. It was observed that for saturated unit weight (γsat) of 11.7 kN/m3 the FOS was lower by 12.5% in comparison to γsat of 16 kN/m3 for 5th raising and by 14% for 6th raising in static condition. Similarly, in seismic condition, the FOS at γsat of 11.7 kN/m3 was observed to be low by 14% than that at γsat of 16 kN/m3 for 5th raising and by 15% for 6th raising. The role of unit weight in influencing slope stability of incrementally raised dykes of slurry ponds has been reported for the first time in this study and it shows that light-weight deposits such as coal ash can lead to low FOS when the failure surface passes through the slurry-deposited material. © 2019, Springer International Publishing AG, part of Springer Nature.